Suggestions welcomed...
I believe that (in my usual- "what the heck, if that doesn't work we'll just have to adapt and overcome"- method of buidling) I may have committed a gaff.
At the risk of being too in-depth: I am dealing with some space limitations so poured a concrete slab as large as my site would allow -roughly 6' wide X 5'6" deep. Atop this foundation was erected a block wall ending in an additional reinforced concrete 'pad'. Finally atop this pad a 5" layer of vermiculite/concrete mixed in the standard 5:1 ratio as the insulating hearth. My error, however is that I topped the entire top surface with the insulating concrete leaving no surface to build an additional 'retaining' wall that would provide space between (it) and the external oven wall to enclose insulation. (Poor description).
However, my belief is that as the igloo style build will sit well inside the outer dimension of the insulated hearth, I will be able to apply insulating concrete to a depth of 8+" over all surfaces. Then, using lath and stucco can enclose the previously exposed 'raw' edge of the insulating hearth when I stucco the entire vertical block surface and oven wall/roof.
Is there crazy thinking going on on my part?

Final question - and yes I prowled the insulation threads - Do any of you really feel strongly enough about the improved insulation between FB's ceramic blanket and insulating concrete to strongly recommend using it? Shipping is exhorbitant but I could pick up one box while in Ca next week and ship it to myself moderately inexpensively and then continue with the concrete mix to finish. Besides, I'd like to support FB for the help they provide.

I help with the second question. Use the ceramic blanket product. Either source through Forno Bravo or look to this local vendor as a possible source for this material. It will likely not be any cheaper. However, you will save the postage.

Not being a great one for picture taking...my hands tend to be awfully grubby. I think this illustrates my question somewhat. I suspect I will have a total of 3.2 photos by the time the project is complete (or abandoned).

The advantage to ceramic fiber blanket and boards is in there insulating properties. 2" blanket on the dome, 2" board under the hearth = 4" of vermiculite or perlite concrete. I would try to source locally, I'm sure that you have a refractory supplier or pottery kiln supplier somewhere close by.

Your issue with the "extra perlcrete/vermicrete" slab layer is covered pretty well in Cdubs' Casa90 Build thread in the Forum's Getting Started section. (I put a link below to the second page of the discussion where his "problem" and yours coincide.) Take a look at how he ended up cutting some of the extra vermicrete skirt away from the slab to secure his enclosure build. He also has a pretty good series of comments/discussion from other members on the insulating blankets and value of additional cement based insulating cover.

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